1. Field of the Invention
The present invention relates generally to aircraft such as tactical fighter aircraft that can employ passive technology for early target detection and target tracking, and specifically to an improved method and system that enhances the. implementation of tactical fighter configuration data and sensor assets for maneuvering or non-maneuvering airborne RF emitters, which represent targets or threats, to enhance the tactical fighter's ability to either avoid or intercept and destroy targets.
Using only a fighter aircraft's passive RF multifunction aperture azimuth measurements along with prescribed fighter aircraft maneuvers, the invention provides an ability to meet passive geolocation quality performance against an active airborne RF emitter (threat. or target). Geolocation involves estimating the target's state vector and error covariance which basically includes range, speed, heading azimuth and elevation.
2. Description of Related Art
Modern warfare requires the airborne defense of military and civilian targets, typically by tactical fighters, whose job is to seek out and destroy incoming enemy aircraft seeking to destroy friendly military and civilian complexes, whether on ground or at sea. At the current speeds and aircraft stealth configurations of potential target aircraft, there exists a critical need for rapid but accurate passive range target speed and heading estimates in order to prioritize incoming aircraft threats, avoid them, and possibly target them. The complex problem provides for a total integration of all of the tactical fighter's onboard and remote assets. The entire weapon system, which includes remote support help with communications and radar, must be completely integrated and used with all the on board aircraft equipment, including ownship and wingmen systems to maximize the ability of the tactical fighter to destroy enemy targets.
A very important aspect of current warfare for airborne weapon systems is to employ passive systems to avoid detection by the oncoming targets. It is felt that current systems based on onboard ownship weapons and information systems have not utilized bootstrap capability of an entire weapon system that. incorporates all of the tactical fighter's on board assets in addition to the remote assets. The prior art shows in U.S. Pat. No. 5,408,541 issued Apr. 18, 1995, a method and system for recognizing targets at long ranges. One of the drawbacks of the system described in this patent is the fact that the system is not completely passive, and does not take advantage of all of the weapon system assets available.
U.S. Pat. No. 6,043,867 issued Mar. 28, 2002, shows a tracking system that includes an apparatus and process for early target detection that uses the passive infrared tracking capability of infrared radiation emitted from a flying target and for generating a succession of line-of-sight (LOS) or LOS rate signals that are stored in a database. The electromagnetic finder in the system is configured to operate at first detection threshold for receiving relatively low magnitude reflections. Estimations are made of LOS and first-stage data, facilitating early steering of the interceptor for dually homing onto the target. Again, there is no bootstrapping of the entire ownship system capabilities to solve the overall problem.
The successful operation and maneuvering of a tactical fighter in an actual battle scenario places a tremendous amount of work on the pilot and flight crews to accomplish a successful operation, intercepting and destroying an enemy bomber or fighter. In addition to the safe operational management of the aircraft itself, there is the requirement of a continuous and instantaneous situational awareness of the threat environment, and especially the early warning detection of targets or potential targets to allow ownship and wingmen to achieve either target avoidance or interception and weapon deployment passively in the most efficient and potentially successful intercept. In today's weapons environment, it is also a requirement that ownship and wingmen typically are in a passive mode to avoid detection themselves from the incoming targets.
Thus, each tactical fighter, which often includes two aircraft, ownship, and wingmen, have configuration data and sensor assets which can be used for passively initializing potential target tracks and provide passive range estimates of estimated quality for these initialized tracks and to sustain or maintain or drop the tracks, whether it be for maneuvering or non-maneuvering incoming airborne RF emitters, which could be either threats or real targets.
The present invention provides for a solution of this problem, which includes providing a method and system for a flyable airborne emitter (target) location solution in the cockpit by bootstrapping batch maximum likelihood (ML), probabilistic data association filter (PDAF), and recursive interacting multiple model (IMM) methodologies that use 1) noisy electronic warfare (EW), 2) interferometer measurements, such as the cosine of cone angle, 3) pulse descriptor word (PDW) data, 4) priority mission data, 5) real time mission constraints, and 6) available real time track information from other on board avionics and off board information sources. By utilizing the present invention, the entire weapon system on board ownship and wingmen abilities are enhanced to attain the most rapid and accurate passive range estimates.
The present invention involves the enhancement and modification in order to bootstrap the approach presented in IEEE paper entitled “Bearings—Only Tracking of Maneuvering Targets Using a Batch Recursive Estimator,” published in IEEE Transactions On Aerospace And Electronic Systems, Volume 37, No. 3, July 2001. The information presented in this article is incorporated into this patent application by reference. The paper approach describes a batch recursive estimator for tracking maneuvering targets from bearings-only measurements in clutter, such as low signal-to-noise ratio targets. The approach was used to combine batch maximum likelihood probabilistic data association (ML-PDA) estimator with the recursive interacting multiple model (IMM) estimator with probabilistic data association (PDA) to result in better tracking initialization, as well as track maintenance results in the presence of clutter. The methodology describes also how batch recursive estimator can be used for adaptive decisions for ownship maneuvers based on target state estimation to enhance target observability.
The present invention provides a method and system that can bootstrap the approach presented in this article to greatly enhance passive range convergence. The present invention also deals with the inner workings of the interacting multiple model.
The high level block diagram defining the IEEE AES paper is shown in FIG. 1. The methodology discloses track initialization (maximum likelihood probabilistic data association filter) and track maintenance (interacting multiple model PDAF with amplitude information) pieces. The real time measurement inputs are noisy angle measurements and signal amplitude. The output is a range estimate and quality factor. This approach will be limited and range conversion slow. The IEEE AES paper approach does make for an excellent basis to develop the invention by bootstrapping architecture as described below. When looking at FIG. 1, the IEEE AES paper approach shows angle and signal amplitude data, which is fed to a track initialization and track maintenance data. The final result is range estimate and quality factor. One of the limitations is that in the IEEE AES paper, only the angle and signal amplitude data are used. The internal design parameters are fixed, so no real time adaptive capability is available.
In current tactical fighter aircraft, for pilot situational awareness, there are various pilot cue analyses that are provided in the form of heads-up display and other cockpit information devices that clearly show numerous variables to the pilot concerning the status of the aircraft and the attitude. Using the pilot cue analysis and the information given to the pilot, both in ownship and wingmen, with the present invention, an entire mission system's functionality can be provided that takes advantage of all the information available to ownship.
This invention provides the innovative use of the interacting multiple model (IMM) Kalman filter-based algorithm in two stages. The ability to meet passive geolocation quality performance against an active airborne emitter (target) using only fighter aircraft passive RF multifunction aperture azimuth measurements along with the prescribed fighter aircraft maneuvers is achieved. The geolocation involves estimating the target state vector and error covariance. Stage one includes monitoring the measurement residuals by processing measured multifunction aperture (MFA) azimuth and elevation when available data over a set of candidate initial state vectors to weed out improbable geolocation solutions (and converge to the most likely) to effectively initialize the Kalman filter state vector. In stage two, the invention continues processing the subsequent angle measurements in the two-model interactive multiple model whereby the airborne target dynamics are modeled as (1) straight (i.e., constant speed and heading) and (2) undergoing maneuver (i.e., heading change) over a brief period of time. The present invention then overall enhances a tactical fighter aircraft's ability to intercept and destroy incoming targets.